Electrical coils formed on integral or tubular core bobbins are well known in the prior art, such bobbins having terminating flanges or cheeks at each end thereof to define a main wire-winding space. The terminal connections for such prior art electrical coils are formed by running wire from the main coil through the flanges to posts on each end of the bobbin, wrapping several turns of wire around the posts, anchoring the wire wound on the posts by soldering, and then severing any remaining wire from the posts.
Fabrication of the terminal connections of these prior art bobbins is cumbersome and time consuming, requiring manual handling to wire the posts and to subsequently solder the wound wire together. Breakage of wire, especially in miniature bobbins utilizing hair-like wire, is another problem prevalent in in these prior art bobbins.
A further problem with the prior art bobbins is that the terminal connections thereof are structurally weak. Such terminal connections are unsuitable for manufacturing applications which exert large stresses on the terminal connections, the large stresses often causing fractures and/or breakage.
A bobbin of unitary construction which overcomes these disadvantages, is described in U.S. Pat. No. 4,380,748 of the present assignee. The '748 patent shows a bobbin of unitary construction having a main winding space for winding electrical wire to form the electrical coil, and at least one further winding space separate from the main winding space for terminating the wire wound on the main winding, thereby forming a terminal connection for the electrical coil. The winding space comprises a tubular winding core defined by spaced apart end cheeks.
The winding core has formed therein a notched annular groove. A cut-out is formed in the tubular winding core, which exposes the hollow core of the winding space and which also forms gaps or breeches in the groove. As wire is wound on the winding space, the gaps in the winding space are bridged by the wound wire to form an unsupported bridging portion, the unsupported wire bridging portion comprising the terminal connection. The wire strands at the bridging portion is soldered together to form terminal connections for the coil wound on the main winding space. The gaps in the winding space ensure that the bobbin is not deleteriously affected by the soldering operation.
While the bobbin described in the '748 patent provides terminals that can be wound and soldered by automated procedures, it will be appreciated that the wire on the winding space which forms the bridging portion thereof is not supported physically, but rather is suspended, and therefore exposed to possible damage during soldering or further handling of the bobbin. Thus, while the invention of the '748 patent provides relatively tough and strong terminal connections, the unsupported bridging wire portions forming the terminal connection are structurally weak, which limits the strength and durability of the terminal connections of the electrical coil. In addition, the soldering connection is localized at the bridging portion of the winding space.